Pore-size acidity

Hettinger et al (7) have presented this staged cracking concept as a useful model for FCC resid catalyst design (figure 4). Based on this model we can envision a very specific Pore Size Acidity Distribution (figure 5), which would be necessary to achieve an improvement in resid conversion. 

Special pore size Acidity Distribution reduces coke and gas formation... 

A preparation of designed catalyst is one of the interest subjects to understand the catalysis. Efforts have been paid for the development of unique preparation method[1] those are metal cluster catalysts derived from metal carbonyls, tailored metal catalysts through organometallic processor and ultra-fine metal particle catalysts prepared by metal alkoxides, etc. These preparation methods are mainly concentrated to design the active sites on support surfaces. However, the property of support itself is also a dominant factor in order to conduct smoothly the catalytic reaction. It is known that some supports are valuable for the improvement of selectivity. For example, zeolites are often used as catalysts and supports for their regular pore structures which act effectively for the shape selective reaction[2]. In order to understand the property of support, the following factors can be pointed out besides the pore structure structure, shape, surface area, pore size, acidity, defect, etc. Since these are strongly correlated to the preparation procedure, lots of preparation techniques, therefore, have been proposed, too. Studies have been still continued to discover the preparation method of novel materials as well as zeolites[3]. 

Mobil MTG and MTO Process. Methanol from any source can be converted to gasoline range hydrocarbons using the Mobil MTG process. This process takes advantage of the shape selective activity of ZSM-5 zeoHte catalyst to limit the size of hydrocarbons in the product. The pore size and cavity dimensions favor the production of C-5—C-10 hydrocarbons. The first step in the conversion is the acid-catalyzed dehydration of methanol to form dimethyl ether. The ether subsequendy is converted to light olefins, then heavier olefins, paraffins, and aromatics. In practice the ether formation and hydrocarbon formation reactions may be performed in separate stages to faciHtate heat removal. 

Acetic anhydride and acetic acid increase the solubiUty of the two phases in each other, and they are employed for the commercial N-nitration of hexamethylenetetramine [100-97-0] (11) to form cyclotrimethylenetrinitramine [121-82-4] (RDX), (CH2)3(NN02)3. Renewed consideration has been given to replacing H2SO4 with an improved soHd catalyst to reduce the environmental problems of disposal or reconcentration of the waste acid and to increase production of desired nitrated isomers. For example, a catalyst with suitable pore size might increase the production of 4-MNT and reduce that of 3-MNT when toluene is nitrated. 

In this appHcation, ZSM-5 acts as a strong, soHd acid, and may be viewed as supported on the surfaces of the crystalline zeoHte stmcture. The older, Friedel-Crafts aluminum chloride catalyzed process for ethylbenzene produces considerably more by-products and suffers from the corrosivity of the catalyst system. Because of the intermediate pore size of ZSM-5, those reactions that produce coke from larger molecules that cannot enter the ZSM-5 pore stmcture are significantly reduced, which greatly extends catalyst lifetime. 

The same type catalyst modified with boron (41), magnesium (42), or phosphoms (43) to reduce the pore size can be used to alkylate toluene with ethylene to produce predominantly -ethyltoluene. Since -ethyltoluene [622-96-8] has the smallest effective diameter of the ethyltoluene isomers, the selectivity to this isomer is favored because it can most easily escape the ZSM-5 pore stmcture. For the same reason, the alkylation of toluene [108-88-3] to xylene [106 2-3] also is favored over the usual acid catalyzed equiHbrium mixture of isomers when it is carried out over magnesium- or phosphoms-modified ZSM-5 (44). 

Freeing a solution from extremely small particles [e.g. for optical rotatory dispersion (ORD) or circular dichroism (CD) measurements] requires filters with very small pore size. Commercially available (Millipore, Gelman, Nucleopore) filters other than cellulose or glass include nylon, Teflon, and polyvinyl chloride, and the pore diameter may be as small as 0.01 micron (see Table 6). Special containers are used to hold the filters, through which the solution is pressed by applying pressure, e.g. from a syringe. Some of these filters can be used to clear strong sulfuric acid solutions. 

Aluminium oxide is available in grades with neutral, acidic and basic reactions, which can also vary in the specific surface area and pore size. This makes the separations achieved vary and care must be taken to document precisely. 

Shifts in the SEC fractionation range are not new. It has been known for decades that adding chaotropes to mobile phases causes proteins to elute as if they were much larger molecules. Sodium dodecyl sulfate (SDS) (9) and guanidinium hydrochloride (Gd.HCl) (9-12) have been used for this purpose. It has not been clearly determined in every case if these shifts reflect effects of the chaotropes on the solutes or on the stationary phase. Proteins are denatured by chaotropes the loss of tertiary structure increases their hydrodynamic radius. However, a similar shift in elution times has been observed with SEC of peptides in 0.1% trifluoroacetic acid (TEA) (13-15) or 0.1 M formic acid (16), even if they were too small to have significant tertiary structure. Speculation as to the cause involved solvation effects that decreased the effective pore size of the... 

Various analytical tests determine zeolite properties. These tests supply information about the strength, type, number, and distribution of acid sites. Additional tests can also provide information about surface area and pore size distribution. The three most common parameters governing zeolite behavior are as follows ... 

The physicochemical properties of carbon are highly dependent on its surface structure and chemical composition [66—68], The type and content of surface species, particle shape and size, pore-size distribution, BET surface area and pore-opening are of critical importance in the use of carbons as anode material. These properties have a major influence on (9IR, reversible capacity <2R, and the rate capability and safety of the battery. The surface chemical composition depends on the raw materials (carbon precursors), the production process, and the history of the carbon. Surface groups containing H, O, S, N, P, halogens, and other elements have been identified on carbon blacks [66, 67]. There is also ash on the surface of carbon and this typically contains Ca, Si, Fe, Al, and V. Ash and acidic oxides enhance the adsorption of the more polar compounds and electrolytes [66]. 

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